The proposed research is directed toward the long-term goal of examining nursing measures in light of the circadian variations of physiological parameters in the body. Specific aims of the study are: Phase I: Pathophysiological Basis for Nursing Interventions for Hypokalemia 1. To compare the differences in phase angles and amplitudes of the cosine wave forms of the circadian rhythms of plasma potassium in normokalemic and hypokalemic rats. 2. To describe the relationships between the circadian rhythms of plasma corticosterone and aldosterone and the circadian rhythms of plasma potassium in normokalemic and hypokalemic rats. 3. To describe the relationships between the circadian variation of red blood cell potassium and muscle potassium and the circadian rhythms of plasma potassium in normokalemic and hypokalemic rats. Phase II: Preliminary Testing of Theory-Derived Nursing Interventions for Hypokalemia 1. To describe the effects of timing dietary potassium replacement with the maximum or the minimum of the circadian rhythm of plasma potassium on the potassium status of hypokalemic rats. Chronic cannulation techniques in rats will provide blood samples every four hours for characterization of the circadian rhythms of plasma potassium, aldosterone and corticosterone in both normokalemic and hypokalemic rats. Erythrocyte potassium, muscle potassium and plasma potassium will be determined from animals at time of sacrifice. Standard computerized cosinor analysis will be utilized to characterize circadian rhythms mathematically and to compare rhythms in normokalemic and hypokalemic rats, providing the scientific basis for nursing intervention studies. Changes in plasma potassium in hypokalemic rats fed potassium-rich food at different times of day will be analyzed to examine the therapeutic benefits of timing dietary replacement of potassium with the circadian rhythms of the body.